Damped turbomachine rotor assembly

ABSTRACT

THE DISCLOSURE ILLUSTRATES A CENTRIFUGAL COMPRESSOR COMPRISING AN INDUCE HUB TELESCOPED OVER AN ADJACENT SHOULDER OF AN IMPELLER HUB. THE INDUCER HUB HAS AN INNER ANNULAR SURFACE WHICH RECEIVES AN ANNULAR RELATIVELY THIN SPLIT RING ELEMENT. WHEN THE COMPRESSOR ROTATES AT HIGH R.P.M&#39;&#39;S THE SPLIT RING FRICTIONALLY ENGAGES THE INNER ANNULAR SURFACE OF THE INDUCER HUB TO DAMP VIBRATIONS.

June 20, 1972 w. c. SHANK DAMPED TURBOMACHINE ROTOR ASSEMBLY Filed Oct. 5, 1970 INVENTOR WAYNE C. SHANK 7 7. 7 ATTORNEYS.

"United States Patent 3,671,140 DAMPED TURBOMACHINE ROTOR ASSEMBLY Wayne C. Shank, Williamsport, Pa., assignor to Avco Corporation, Williamsport, Pa. Filed Oct. 5, 1970, Ser. No. 77,969

- Int Cl. F01d 25/28 U.S. Cl. 416-183 3 Claims ABSTRACT OF THE DISCLOSURE The disclosure illustrates a centrifugal compressor comprising an inducer hub telescoped over an adjacent shoulder of an impeller hub. The inducer hub has an inner annular surface which receives an annular relatively thin split ring element. When the compressor rotates at high r.p.m.s the split ring frictionally engages the inner annular surface of the inducer hub to damp vibrations.

The present invention relates to turbomachine rotor assemblies and more particularly to assemblies of the type that have provisions for damping.

In the gas turbine art there have been numerous devices developed for minimizing vibration in rotor assemblies. For the most part these damping arrangements utilize the principle of frictional engagement of the tips of adjacent blades on hub assemblies.

An example of this approach may be found in the US. patent to Birmann No. 2,405,283. This patent illustrates a machined-away shoulder adjacent the inner portions of one set of blades so that only the tips of the blades abut adjacent blades. The blade assemblies are held with suflicient axial force to cause the edges of the blades to frictionally engage and damp vibrations. There are many other approaches to this problem that utilize this principle. However, they all suffer from the disadvantage of either disturbing the flow path through the impeller or requiring expensive manufacturing techniques.

Therefore it is an object of the present invention to provide a highly simplified and economical means for damping a turbomachine rotor.

The above end is achieved by a damped turbomachine rotor comprising a generally annular hub spaced outward from its axis of rotation and having an inner annular surface. An annular, relatively thin ring element is received within and conforms to this surface so that centrifugal force urges the ring member into frictional engagement with the inner surface to damp vibrations in the blades.

The above and other related objects and features of the present invention will be apparent from a reading of the description of the accompanying drawing and the novelty thereof pointed out in the appended claims.

In the drawing:

FIG. 1 is a longitudinal sectional view of a centrifugal compressor rotor assembly embodying the present invention;

FIG. 2 is a view taken on lines 22 of FIG. 1 which illustrates the fundamental mode of vibration of the compressor hub;

FIG. 3 is a perspective illustration of a split ring element incorporated in the impeller of FIG. 1.

Referring now to FIG. 1, there is shown a centrifugal compressor rotor assembly with which the present invention may be used. The rotor assembly comprises a first generally annular shaped hub 12 spaced outwardly from its axis of rotation A. The hub 12 has a series of radially extending blades 14 to form the impeller portion of the rotor assembly 10. A second hub 16 is positioned upstream 3,671,140 Patented June 20, 1972 ice I of the hub 12 and is also annular and spaced outwardly from the axis of rotation A. An annular surface 15 is formed on the inner side of hub 16. Hub 16 has a series of inducer blades 18 which extend radially outward but are cambered so as to efiiciently receive air from an axially directed inlet, shown in phantom and designated by reference character 21. The inducer blades 18 are spaced from but correspond with the impeller blades 14 to form a generally annular accelerating flow across the centrifugal compressor rotor 10.

Hub 12 has an elongated shaft portion 26 over which hub 16 is telescoped. A tapered pilot diameter 28 on the elongated shaft portion 26 and a corresponding tapered diameter 30 on the inducer hub 16 centers it on elongated shaft portion 26 of hub 16. An internally threaded nut 32 is screwed onto the threaded portion 35 of the elongated portion 26 by a suitable tool which engages slots 34 in element 32. Element 32 holds the inducer hub 16 against a shoulder 20 on the impeller hub 12.

An annular relatively thin ring element 36 is received within and conforms to the inner annular surface 15 of hub 12. Preferably the ring 36 is split at 38, as shown in FIG. 3, and formed to have an outside diameter slightly greater than the diameter of the inner annular surface 15. Element 36 is then compressed for insertion into the inner annular surface 15 and once in position is yieldably maintained in place.

In operation the centrifugal compressor rotor assembly 10 rotates at a high rate of speed. Due to many exciting forces the blades 18 and 14 tend to vibrate in their several modes. As shown in FIG. 2, the resultant vibration causes deformation of the inner annular surface 15 of annular inducer hub 16 from which the blades 18 extend radially. The deflection of the hub for a swing of blades 18 to the left is shown in exaggerated proportion by the phantom lines of FIG. 2. It can be seen that this deflection generally resembles a sine wave superimposed on the annular shape of the inner annular surface 15. A swing of the blades to the right causes a similar deflection in the opposite direction.

The ring element 36 is urged radially outward by centrifugal force into frictional engagement with the deflected portion of the inner annular surface 15. As the blades swing the resultant ridges and valleys in the inner annular surface rub against the ring element 36. The resultant frictional engagement absorbs energy created by the deflection of the rotation of the blades. Damping at this radially inward portion requires a high degree of energy. However, for a speed of over 50,000 r.p.m. the weight of the split ring is magnified approximately 100,000 lbs. times its radius in inches. Even for a small spacing from the axis of rotation the ring element 36 exerts a suflicient outward force to effectively damp vibrations.

While the present invention has been described in connection with the inducer portion of a centrifugal compressor, it is believed that those skilled in the art can adapt the invention to other turbomachine rotors, such as axial flow type or centripetal turbine assemblies without departing from the spirit and scope of the present invention.

Having thus described the invention, what is claimed as novel and desired to be secured by Letters Patent of the United States is:

1. A damped turbomachine rotor assembly adapted to rotate at relatively high rates, said rotor assembly comprising:

a generally annular hub spaced outward from its axis of rotation having an outer surface defining the inner bounds of a flow path for fluid and an inner annular surface;

a plurality of blades extending radially outward from the outer surface of said hub substantially radially outward from said inner annular surface, said blades being subjected to vibratorybending forces thereby References Cited producing deflections in said interior surface; and UNITED STATES PATENTS an annular relatively thin ring element received within the inner annular surface of said hub member and 5 3'383O91 5/1968 Newland 416-242 conforming thereto, whereby centrifugal force urges 3356339 12/1967 Thomas a 416 500 said ring member into frictional engagement with the 3531216 9/1970 l 416 244 inner surface of said hub for damping vibrations. 2356605 8/1944 Meimmghaus 416-498 2. A rotor assembly as in claim 1 wherein said ring ele- 11/1953 Gnffith 416-400 ment is split and has an outside diameter slightly larger 10 2941780 6/1960 Von der Muen et 416-500 than the diameter of said inner annular surface whereby 2,970,808 2/1961 PP 416199 the ring element is compressed forinsertion into said in- $304,052 2/1967 Wamet et a1. 416-193 ner annular surface and is yieldably maintained in position. 3,384,345 9 Neath 6t 21 416l83 3. A rotor assembly as in claim 1 wherein said hub and 7 8 /1971 Musick 416-190 blades comprise an inducer of a centrifugal radial out- 5 flow compressor and said rotor assembly further com- MARTIN P. SCHWADRON, Primary Examiner prises:

a downstream radial outflow impeller hub; SCHIMIKOWSKI Asslstant Exammer a plurality of blades extending radially outward from said impeller hub, said blades being out of contact 20 U.S. C1. X.R. with said inducer blades. 416244, 500 

